The word 不是 is formed by directly combining two fundamental characters: the common negation particle 不 (bù), meaning "not", with the verb 是 (shì), meaning "is/am/are" or "to be". It is a straightforward, literal fusion where the negator is placed immediately before the verb it negates, creating a single conceptual unit that means "is not" or "to not be". This construction represents the most basic and logical way to deny identity or equivalence in the language, mirroring a simple algebraic negation of the core verb for "being".